Experts are surprised and skeptical of a Colorado judge's ruling that Aurora theater shooter James Holmes could be subjected to a "truth serum" if he decides to plead not guilty by reason of insanity.

The term used by Judge William Sylvester earlier this week in his court ruling was that a "narcoanalytic interview" could be employed to determine if Holmes is genuinely insane.

"The last time I had read that term being used as if the practice had any validity was decades ago," said Alison Winter, a professor of history of science and medicine at the University of Chicago who has done extensive research on "truth serum."

The idea behind this nearly century old tool is not that it forces people to tell the truth, but that it lowers their inhibitions and presumably makes them more inclined to talk.

Experts take issue with the technique, but acknowledge the "seductive" nature of the idea behind it.

Sylvester's court order does not specify what drugs could be used on Holmes, but it would likely be a drug like sodium amytal or sodium pentothal.

A judge entered a standard not guilty plea on Holmes' behalf on Tuesday. He is accused of killing 12 and wounding dozens in an Aurora movie theater on July 20, 2012. The option of not guilty by reason of insanity is still open to Holmes and his attorneys.

"It shall also be permissible to conduct a narcoanalytic interview of you with such drugs as are medically appropriate, and to subject you to polygraph examination," Sylvester wrote in the order. The test could be used to help determine Holmes' mental condition.

Defense attorneys filed a motion opposing the technique, but the judge signed the order that permits it.

"It's an extraordinarily unusual procedure to use," Dr. Steven Hoge, a clinical professor of psychiatry at Columbia University in New York, told ABCNews.com. "The fact that they've linked it to the use of polygraph makes me concerned that they do believe that it is indeed a 'truth serum' and there's no evidence to support that."

Hoge said that are no controlled studies that demonstrate that information obtained under narcoanalysis is reliable.

"The idea that sodium amytal is a truth serum is not correct," he said. "It's an invalid belief. It is unproven in its ability to produce reliable information and it's not a standard procedure used by forensic psychiatrists in the assessment of the insanity defense, nor is polygraph."

Hoge once administered "truth serum" himself in Massachusetts in the 1980s.

"I've used it once in an attempt to recover memory from a severely intoxicated man who couldn't recall what he had done while intoxicated," Hoge said. "It was unsuccessful."

The drug was administered to the inmate in a hospital setting because it can result in the suppression of breathing, Hoge said. An IV drip was inserted and sodium amytal was injected into the patient who then answered questions.

Winter said the first "truth serum" was introduced by Robert House, a Texas doctor who was using it as an obstetric anesthetic during labor around 1915.

He discovered that when the drug administered to women during childbirth was used at a lower dose--but not low enough for patients to lose consciousness--people would be in a state where he thought "they wouldn't censor themselves," Winter said.

"He wasn't thinking of it as an interrogation tool," Winter said. "Lots of people laughed at him, but there was quite a bit of interest in whether you could get people to deliver the truth."

Winter said that in the 1920's and 1930's the truth serum became "a kind of shadowy police tool."

"The results of the supposed truth serum were not admissible in court, but they were sometimes used as interrogation aids," she said. "There isn't a lot of documentation of this, but there's enough to see that it was done."

During World War II, the drug was sometimes used as a way of identifying people who were faking being shell-shocked.

Since then, mentions and use of the drug have been very rare.

James Holmes Could Be Subjected to "Truth Serum"

In his book, Judge Sam Amirante, who was John Wayne Gacy's defense attorney, wrote that sodium amytal was used on Gacy. Amirante said in an interview that Gacy's "personality was so strong that he was actually fighting off" the drug. Many accused Gacy of lying about taking the test.

There have been other cases where "truth serum" was allegedly administered and ruled inadmissible in court.

Experts say that one of the issues with using the drug is that it's very difficult for questions not to be suggestive and lowered inhibitions can lead to true as well as false information.

"Understanding of memory has shifted a lot over the years," Winter said. "Memories are really volatile and if you use a technology like drugs or hypnosis, you can get information that's valid, but along with it you get a lot of information that isn't, that's just a response either to something suggestive in how you're asking the question or else just something random that you have no ability to even identify."

"You can't tell the difference between the real stuff and the fabricated stuff," she said.

Despite doubts over the technique's acceptability, Winter understands the intrigue with the idea.

"It's a very seductive idea and it's something that people keep coming back to," Winter said. "We've had it for almost 100 years."

"The idea that the truth about what a person is like or the truth about what they did is just sitting inside their body waiting to be almost surgically extracted...it is just so enticing if you desperately need that information," she added. "So I think we keep coming back to it, but then we also keep rejecting it."